1. Field of the Invention
The present invention relates to a method of producing a metal oxide fiber and, more particularly, to a method of producing a metal oxide fiber employing a sol/gel process, and metal oxide fibers produced according to the method.
2. Description of the Prior Art
Conventionally, attempts have been made to apply a metal oxide material to functional devices by utilizing various characteristics of the metal oxide material. For example, it has been known that (Pb, La) (Zr, Ti)O.sub.3 (hereinafter referred to as PLZT) has a perovskite crystal structure and exhibits high secondary electro-optic effect (Kerr effect), which makes it possible to use the metal oxide material in various applications such as optical shutter, optical modulator, and ferroelectric memory. Also, it has been known that Pb(Zr, Ti)O.sub.3 (hereinafter referred to as PZT) has a perovskite crystal structure and exhibits high piezoelectric effect, which makes it possible to use the material in such an application as actuator.
If such a metal oxide could be formed into a fiber form, the range of applications of the metal oxide would be broadened, and this would make it possible to develop a novel device. For example, by arranging PLZT fibers in array it is possible to provide an optical shutter device capable of processing plural beams in parallel.
A method of producing a metal oxide fiber is reported in, for example, a journal "FERROELECTRONICS", 1990, Vol. 1112, pp 283-307, in which a report on the production of a PLZT fiber by sol/gel process. The term "sol/gel process" used herein means a method of producing a glass phase metal-oxide material or sintered metal oxide material which includes the steps of preparing an organic or inorganic metal compound in the form of solution, effecting the hydrolysis and polymerization reaction of the compound in the solution thereby to form a particulate-containing sol, converting the sol into a gel which contains a liquid or gas present in interstices within a solid-phase skeletal structure, then heating the gel.
According to the technique described in the report, lead acetate hydrate, lanthanum acetate hydrate, zirconium n-propoxide and titanium n-propoxide are used as starting materials and, after a solution in which the materials are uniformly dissolved is obtained, an acid catalyst is sued to effect hydrolysis and polymerization, the resulting solution being concentrated to give a high-viscosity sol having a spinnable characteristic. The report says that a gel fiber of PLZT can be produced from the high-viscosity sol by forming the sol into fiber form.
In the above noted technique, however, the presence of the acid catalyst in the sol allows continued progress of hydrolysis and polymerization even after the sol exhibits a spinnable characteristic, and this poses a problem that the useful life of the solution is shortened.
Another problem is that an organic matter residue is present in the interior of the fiber, so that the organic matter is vaporized in the heat treating stage, which results in the formation of voids having an air gap of about 100angstroms or more which can hardly be removed even when heat treatment is carried out at a high temperature for a long time period. The presence of such voids in the material poses a further problem that the electro-optic characteristic and light transmittance of the material are lower than a normally expectable level when the fiber is in use.